Leishmaniasis refers to a constellation of disease syndromes caused by the Leishmania spp. protozoa. Leishmaniasis affects persons residing in endemic regions, including the sites of recent and ongoing US military activities in the Middle East. Common forms of leishmaniasis include visceral leishmaniasis (VL) caused by Leishmania infantum or L. donovani, or cutaneous leishmaniasis (CL), often due to L. major or L. tropica in the Middle East and northern Africa. A common feature of the different forms of leishmaniasis is their propensity to cause asymptomatic infections, particularly in healthy hosts. The ratio of asymptomatic to symptomatic leishmaniasis varies from 6.5:1 in to >100:1 in different endemic regions. Due to the poor ability to recover parasites in culture and imprecise markers for infection, diagnosis of asymptomatic infections can be elusive. The mechanisms and the consequences of these occult infections are largely unknown. Methods to recognize asymptomatic leishmaniasis have improved, leading to a recent report that nearly 20% of soldiers deployed to endemic regions of Iraq during 2002-2011 have evidence of ongoing L. infantum infection in their bloodstream. Leishmaniasis is a disease associated with chronic inflammation, and we do not know the consequences of long-term asymptomatic infection with this protozoan. Furthermore, asymptomatically infected soldiers are at risk for developing symptomatic disease if immunocompromise occurs in later years. All eukaryotic cells release extracellular vesicles (EVs) into their environment. The subset of EVs called exosomes are known to transmit bioactive proteins, microRNAs, metabolic enzymes and lipids between cells or throughout the bloodstream. Our preliminary studies show that exosomes from L. infantum induce an inflammatory state in human cells and in murine skin, which phenocopies the inflammatory state induced by the infectious parasite. This finding led us to hypothesize that at least some of the inflammatory responses induced during leishmaniasis are caused by exosomes released from intact parasites or from leishmania-infected cells. Aims of the current application are: ? Aim #1: To document the differences in protein and miRNA content of EVs released by different species of Leishmania, or by nave or Leishmania-exposed myeloid cells. Aim #2: To query to what extend the components of EVs are responsible for host inflammatory responses in murine models of leishmaniasis, both locally and systemically. Aim #3: To document differences between EVs circulating in serum or released in urine of healthy humans or people with asymptomatic or symptomatic Leishmania spp. infections. Through these studies we will address the hypothesis that Leishmania infection causes the release of EVs whose contents induce many of the systemic inflammatory responses associated with Leishmania spp. infections. We hope that these findings will inspire the design of novel therapeutic and/or diagnostic approaches to leishmaniasis.